A. Technical Field
The magnetic bubble device described in Bell System Technical Journal, 46, 1901 (1967) exemplifies a family of stepping memories in which bits are caused to traverse discrete positions by moving bias of a level inadequate to nucleate but sufficient to propagate. Devices of this nature are expected to play an increasing role and to serve functions of apparatus in which bit movement is brought about mechanically (magnetic tape, disc).
In addition to serving as memories, such devices may be caused to perform logic functions in which bits may attract, repel, multiply, etc.
Another category of devices sometimes serving as displays depend upon luminescence which may be induced electrically. Again, such luminescent devices may serve memory functions. Since "bits" may be visible, they may also serve display functions--e.g., alpha numeric or pictorial.
A combination of function is visualized--i.e., memory or logic devices with self-contained, visible read out.
B. History
A form of electroluminescence depends upon flowing electrons traveling within an insulated electroluminescent medium under the influence of an applied ac bias. The bias creates an electric field which accelerates electrons, with luminescence resulting from collisions with luminescence centers. Photons emitted from such center may be in the visible band. In a particular material, manganese-doped zinc-sulfide, light emitted is yellowish--of a center wavelength of approximately 5,800 Angstrom units.
In Topics in Applied Physics, Vol. 17, Springer-Verlag, p. 197, it is shown that light emission may be produced in such material responsive to applied electrical pulses above a well-defined threshold value and that a hysteresis in emission versus field can be observed.
Further, in Applied Physics Letters 31, 452 (1977) it is shown that emission from ZnS:Mn occurs in filaments that are less than 1 .mu.m in diameter, having negative resistance characteristics and which are either off or on in a state of saturated emission. In addition, experimental evidence for current filaments in Ge is reported in Journal of Applied Physics 33, 995 (1962) and it has been shown in
Proceedings in the Physical Society, 82, 954 (1963) that such filaments will form in any material with a negative resistance characteristic. It is a simple step from this observation to state that visible emission will result from a current filament if the material is also electroluminescent, e.g., ZnS:Ag, GaAs, GaP etc. Recently, in Electronics, July 6, 1978, p. 33. it was reported that experimental work on the ZnS:Mn system revealed properties of device interest--i.e., useful mobility, stable bias levels, useful lifetimes, etc. It was also suggested that while the phenomenon was of interest for devices functioning in the manner of bubble memories, techniques for reliably stepping bubbles from position to position had not been found.